I don't think anyone will have a definitive answer to my problem - but - all suggestions will be gratefully received.
For the past four years, I have an occasional CAN issue which is getting more and more frequent.
Maybe after 2 miles, may be after 50 - engine hot - battery charged - no "apparent" problems.
Then :
Gearbox Fault + amber light. Limp mode (4th gear only)
About a minute or so later - dashboard like Christmas tree, engine fault, TRAC control, handbrake warning light, no temp gauge, rev counter, ACC etc.


When connected to SDD - Codes are
P1638, P1642 & P1797 plus CCM : "the request cannot be processed due to a bad specification or missing parameter"


I assume the "missing parameter" is engine temp, so I'm not concerned about that one, but any ideas ??
I don't think it is battery related - happens long after car has been driven some distance and battery is fairly new anyway.
DTCs point to a fault in CAN between TCM & ECM but all connections look good at first glance.


Bottle of virtual champagne to the first correct diagnosis !!

 

Maybe an actual CAN problem... chafed wire? Poor connection?

If it's intermittent it's likely to be tough to find. Might get lucky measuring CAN signals or just checking the terminating resistance (60 ohms) while wiggling various wires etc.

 

JagV8- Fair point, but the TCM & ECM are a few inches apart so a chafed wire or loose connection seems unlikely. I don't rule it out - we're all aware how temperamental the electrikery in these cars can be. I suspect it's an internal problem with the ECM or TCM but that's megabucks to repair or replace, so I'm clutching at cheaper straws if possible !!

 

My commiserations. Intermittents can be a real PITA, and the nature of this beast is going to give you all manner of weird stuff

You might bring the Major Instrument pack into the puzzle. DTC summary for P1638 is:

Fault
CAN INST token missing

Default Action
None
Engine speed and coolant temperature data missing at instrument pack

Possible Causes
INST failure
CAN open circuit fault – INST to ECM
CAN short circuit fault
ECM failure

They do fail, although apparently not often. Try removing and reseating the two connectors at the bottom. I'm sure I've seen a Rev. Sam video that shows how to get to these. Your LHS connector may be yellow.




HTH,
Mike

 

I think you should at least open up the ECM case and visually inspect it for leaking electrolytic capacitors.

 

Mike & Steve.
Good advice there - thanks.
Will report back if I find anything noteworthy.

 

The CAN data packets pass thru the Shift Module circuit board before getting to the instrument pack. The small white pc board connector on that board begins to break off after years and years of service because of cable harness weight or if someone has worked in the console in that area. The white connector breaking loose, will cause data packets to be dropped/lost and can result in the errors you are seeing. Sometimes, you can put light pressure on the connector and cause the errors to go away while the pressure is being applied.
If this is your problem, the fix is to remove the white connector and solder the cable harness wires directly to the PC board. A pictorial procedure for doing this is on the board.

 

cybercg
Thanks for that. I have decided to start in that area - a superficial inspection shows that there is considerable wear on the two "lever operated" microswitches in the J Gate. (Looks like one of the little levers has actually dropped off) and I am also aware that the shift module is on the CAN circuit as a 'listener' so ....... at not too much expense, both will be replaced with brand new. That may, or may not, solve the problem - but it's as good a place as anywhere to begin the detective work !

 

This may help:

https://www.jaguarforums.com/forum/x...1797-a-101961/